Apparatus for the production of phthalic anhydride and benzoic acid



Aug. 3,1937 M. SCHARFF ET AL APPARATUS FOR THE PRODUCTION OF PHTHALIC ANHYD 2 Sheets-Shet 1 Fresh Cai'al oi.

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M. SCHARFF ET AL APPARATUS FOR THE PRODUCTION OF PHTHALIC ANHYDRIDE AND BENZOIC ACID Original Filed Aug. 14, 1929 2 Sheets-Sheet 2 Max I 'Scha'rff' Johannes ,Bmde, dam-156d Adolf Johannaen' J'oaef Re icha'rt INVENTORS ATTORNEY Patented Aug. 3, 1937 I UNl-TED STATES arrana'ros ron THE PRODUCTION 2,088,929 PATENT OFFICE PHTHA LIC, 'ANHYDRIDE AND BENZOIC ACID Max Schari'l, Heidelberg, Johannes Brode, de- 1 ceased, late oi." Ludwlgshaten-on-the-Rhine,

by Kithe Brode, administrat'rim-Ludwigshafenon-the-Rhine, and Adolf Johannsen and Jose!- Belchms Ludwlgshaien-on-the-Rhine, Ger-- many, assignors to I. G. Farbenindustrie Ali-- tiengesellschait, FrankIort-on-the-Main, Ger- :many

Application November 9, 1933, Serial No. 697,302. I which is a division of application August 14,

1929, Serial No. 385,859.

Divided and this application June la, 1935, Serial No. 26,530

vention relates to apparatus ior'purifying the phthalic anhydride, thus rendering it possible to separate it in a pure state, which apparatus may also be used for the treatment of the phthalic anhydride vapors with a catalyst splitting oil carbon dioxide, whereby the phthalic anhydride is converted into benmic acid. Catalysts suitable for this conversion into benzoic acid are described and claimed in the application for patent by Johannes Brode and Adolf Johannsen, Ser. No.

149,520, flied November 19, 1926. The process for the purification of phthalic anhydride is generically described and claimed in the U. 8. Patent No. 9 .915, granted December 4th, 1 1928, to

Johannes Brode and Adolf Johannsen. A specific method of making benzoic acid, in which the gas mixture containing phthalic' anhydride is first passed over a puriiying mass or over a catalyst for making benzoic' acid, which is poisoned and therematter of the u. s. Patent No. 1,889,945, dated December 6th, 1932. The present invention chiefly relates to apparatus suitable for carrying out the processes of the aforesaid patents and appli- 35 cation for patent.

We shall now describe our invention by reference to the production of benzoic acid from phthalic anhydrideJ I While the production of phthalic anhydride by 4 the catalytic oxidation of naphthalene is a highly exothermic reaction, the conversion of the phthalic anhydride into benzoic acid proceeds with only a slight disengagement oi heat. the gases leaving. the oxidation catalyst are dir'ec'tly subjected to the treatment 'with the catapass the gases leaving the oxidation catalyst with 55 a temperature 01' about 400 C. over the catalyst August 14th, 1929. More particularly the inins the catalyst in a counter-current to the gases by reduced in its acitivity, forms the subject Since a capable of splitting of! carbon dioxide directly or after slightly cooling them, which does not present any difilculties ln'practice. Means for controlling the temperature during the decarboxylation need not be provided, but the gases can be brought to reaction in a simple vessel filled with the catalyst, for example inan apparatus somewhat similar in appearance to a shaft furnace.

The conversion oi the phthalic, anhydride into benzoic acid is, however, attended with the difllcuity that the catalysts are very liable to poisoning by sulphuric acid vapors which are formed in the oxidation by the combustion of organic impurities/containing sulphur which are present in com- 15 mercial naphthalene. As has been pointed out.

in the said U. S. Patent No. 1,889,945 this poisoning action of the gases is-counteracted by first contacting the gases with a catalyst which has already been poisoned to some extent by sulphuric acid, but which is still capableof taking up considerable amounts of sulphuric acid, and only then contacting the gases with fresh catalyst. This process is preferably carried out by conduct either continuously or periodically; In the same way highly active catalysts of high value can be protected by first passing the gases through masses which have a substantially lower catalytic activity and are much cheaperand which take up. the sulphuric acid. Examples 01. such purifying. masses are, for example, pumice granules,

, zeolites and the like. In such processes it is advantageous to pass at least the purifying masses in counter current to the gases and our invention relates more particularly toapparatus. for conducting the catalyst or purifying masses in counter-current to the gases in a reliable manner.

Our invention will be'fully described with reference to the accompanying diagrammatical 40 drawings which show some forms of apparatus suitable for carrying out our invention. In the said-drawings Figure 1 represents a vertical section through one form of apparatus. Figure 2 represents a plan view of one structural element or the apparatus shown in Figure 1. Figure 8 'il- .iustrates a modified form of apparatus and Fig-' ure 4 is a cross-section on the line A-A, Figure 8.

Referring first to the modification shown in Figure 1, I is a cylindrical vessel which is filled with a catalyst 2. The catalyst is supported by a sieve-plate 3 which is shown in detail in Figure 2..

As will be seen from said Figure 2, the said sieveplate is provided with 'a number oflarge sector- Shaped holes 4. Below the said sieve-plate 3 there is rotatably arranged a similar sieve-plate 5 also provided with sector-shaped holes. The said sieve-plate 5 can be rotated around the axle 6 by means of the gear-wheels I and the handle 5 8. When the apparatus is in use the two sieveplates 3 and 5 are usually so positioned that the sector-shaped holes of the one plate do not coincide with those of the other plate, that is the two plates form a substantially continuous sieve supporting the catalyst. The gases are admitted by a tube 9 and pass from the chamber I through the said sieves and through the catalyst. They are withdrawn from the upper part of the vessel by a tube ll. When the catalyst is to be removed from above the sieves, the lower sieve 5 is turned so that the sector-shaped holes in the one of the plates coincide with those in the other and the catalyst particles fall down into the chamber ill where they collect and from which they can be withdrawn by means of the sluice 02. Fresh catalyst is supplied into the reaction vessel by means of a hopper i3 and a sluice M. In order to impart the layer of catalyst a uniform level within the vessel l, a steel-brush I5 is arranged therein which can be rotated around the axle i6. Preferably the sluice H is provided with an electric heating device which is not shown in the drawings and by which the fresh catalyst is heated so far as to avoid condensation of phthalic anhydride or benzoic acid on its surface. It will be seen that in the said construction the used catalyst, which is. poisoned to some 'extent 'by sulphuric acid vapors, is always maintained in the lower portion of the vessel i and is brought into contact with the gases first. Only the purified gases come into contact with the fresh catalyst present in the upper part of the vessel l. The said vessel I is surrounded by a chamber ll which serves for heating the vessel and catalyst when putting the apparatus into operation. A'

heating medium, for example hot combustion ases or heated air can be admitted into said chamber H by means of the tube l8 and withdrawn therefrom by the tube 20. The said chamher I! is provided with a spiral-shaped partition 2|, whereby the heating gas is compelled to travel a screw-shaped path.

It will be understood without further explanation that the apparatus described may be modi-' fled in a great variety of ways without departing from the scope of our invention. For example, the sieve-plates 3 and 5 may be provided with openings of another shape than that of a sector, for example, they may have a circular or elliptical shape. Further the lower plate 5 need not be rotated, but the large holes in the two sieveplates may also be brought to coincide by moving the plate 5 in a linear direction. Sieve-plate systems constructed similar to a Venetian blind may also be used.

Referring to Figures 3 and 4, Figure 3 illusare admitted by the tube 9 and are divided throughout the catalyst by means of the annular 70 chamber 22 which is free from catalyst and from which they are admitted to below a number of inverted v-shaped metal bars 23 which serve for dividing them throughout the catalyst. The said metal bars are arranged so that holes of 'substam- 15 tial width are formed between them, which holes permit spent catalyst to pass through. For example, the bars may be arranged radially in the reaction vessel. The spent catalyst is withdrawn by means of the sluice l2, similar to the arrangement shown in Figure 1. In order to prevent the catalyst in the vessel I from falling more rapidly in the center of the vessel than it does near the outside thereof, we prefer to arrange in the lower part of the vessel a stopping device 24 which may be made of sheet-metal, for example, and offers a certain resistance to the downwardly directed flow of catalyst in the center of the vessel.

It may be noted here that all apparatus described in the foregoing are provided with a heat insulation in order to prevent losses of heat. This insulation is not shown in the drawings for the sake of greater clearness. Also the apparatus are provided with means for controlling the temperature which are also not shown in the drawings. ,In the same way as hereinbefore described for the production of benzoic acid, the apparatus may be used for the purification of phthalic anhydride by contact with solid masses absorbing sulphur compounds, as for example pumice stone, silica gel, zeolites, bauxite and the like. In such case the gases leaving the oxidation catalyst are cooled before entering the purification apparatus so far that no catalytic action of the, purifying masses takes place. In this connection it may be pointed out that the said purifying masses possess to a small extent the property of splitting ofi carbon dioxide and of producing benzoic acid when used at high temperatures. Further the power of the said masses of absorbing sulphuric acid is higher at lower temperatures. However, the temperatures should not be so low that separation of the phthalic anhydride vapors contained in the gases takes place and the most suitable temperature is therefore about 200 C. By the separation of the sulphuric acid the formation of r oxidation of naphthalene, which comprises a vessel, a pair of substantially horizontal adjacent plates in said vessel, said plates having a plurality of holes sufllciently small to prevent the free passage of solid material and each having at least one hole sufficiently large to permit said solid material to pass therethrcugh, the upper of said plates being fixed in said vessel and the lower being rotatable in a plane parallel to the upper the upper and in the lower part of said vessel.

MAx SCHARFF. xii'rmz BRODE, Admtnlstrctrix 0/ Johannes Brode, Deceased.

. ADOLF JOHANNSEN. I

JOSE! REICHAR'I'. 

